Resistive RAM (RRAM) cells are memory devices that store data based on the resistance of the RRAM cell (i.e., the resistance between electrodes of the RRAM cell). For example, a RRAM cell in a low resistance state (referred to as a “SET” state) may correspond to a logic “1” and a RRAM cell in a high resistance state (referred to as a “RESET” state) may correspond to a logic “0.” Many types of RRAM cell technologies require bipolar voltages to place the RRAM cells in a particular state. For example, applying a positive voltage across the terminals of the RRAM cell places the RRAM cell in a SET state. In contrast, applying a negative voltage across the terminals of the RRAM cell places the RRAM cell in the RESET state. FIG. 1 is a graph 100 illustrating current versus voltage characteristics for an exemplary RRAM cell, according to some embodiments. As illustrated in FIG. 1, VSET-min is a minimum positive voltage across the terminals of the RRAM cell (e.g., +0.25V) that is required to place the RRAM cell in the SET state and VRESET-min is a minimum negative voltage across the terminals of the RRAM cell (e.g., −0.08V) that is required to place the RRAM cell in the RESET state. When the RRAM cell is in the RESET state, the resistance of the RRAM cell is RRESET (e.g., 1M Ohms) and when the RRAM cell is in the SET state, the resistance of the RRAM cell is RSET (e.g., 10K Ohms).
For performance reasons, it would be desirable to be able to set and reset different cells in an array of RRAM cells concurrently. However, since bipolar voltages are required to set and reset existing RRAM cells, negative voltage charge pumps are required, which complicates the design of the array of RRAM cells. Thus, it would be highly desirable to provide an array of RRAM cells in which different RRAM cells coupled to the same word line can be set and reset concurrently without using negative voltages. It would also be desirable to read and write RRAM cells coupled to the same word line in the array of RRAM cells without having to change biasing conditions.
Like reference numerals refer to corresponding parts throughout the drawings.